welcome back to national five biology we're staying with unit one cell biology today and we're going to be moving on to kiria tube which is transport across cell membranes so from Kyra one you should hopefully remember that all the cells who had a cell membrane you should hopefully remember the cell wall that we looked at in some of the cells and it was made up of cellulose and it was fully permeable I said we would covered the cell membrane later on in our key area so today we are going to look at the cell membrane the cell membrane is termed selectively permeable and that's a really important word because it means that some molecules can pass through the cell membrane in or out of the cell and some molecules can't it has some form of control over what can pass through it what you ask need to know is the structure of the cell membrane so this diagram the bottle here shows the two molecules that make up the cell membrane there are phospholipids which are the sort of tadpole-like structures here and there are proteins which are the the big blobs that you find dr. Tolin you need to know both these and be able to illustrate it potential in our diagram what you all seem to know is like I've seen some molecules pass into the cell or else in the cell and some can't so you need to know some examples of what can move through the cell membrane so some things that are required by the cell that need to move into the cell from the outside are glucose oxygen and amino acids some molecules need to move from inside the cell to outside the cell and the ericon dioxide and urea just waste products I try to remember this a bit like what we need we need glucose an option and we release carbon dioxide and urea so it's very similar in that aspect all those molecules can pass through the membrane one task that we tend to do in the classroom they'll talk free here is to put a solution of glucose starch inside the screen tripping which is a slightly variable plastic that illustrates the cell membrane if you put that into a beaker full of water you can look and see if the molecules from glucose and starch eventually diffuse through the membrane like a cell membrane into the water so essentially if you put this bag of glucose and starch into the water at the start if you tested the water for the presence of starch you would find there was no starch and you would also find that there was no glucose this is because it's still inside the cell membrane however as time moves on you would find that something's a bit different you'd find that there would still be no starch in the water but there is a trace of glucose in the water the glucose has moved through the semi parable or a slightly parable membrane into the water the starch forever has not moved them this is because starch is too big to move through the slide to play Paramaribo membrane this is just an example of how some molecules can move through it but some cannot so again selectively permeable membranes some molecules can move through the membrane to look at this process that I mentioned there or diffusion we look at something called the concentration gradient now if you look at this diagram here are you imagine this triangle here are just a hill at the top of the hill is a high concentration of a substance say for example glucose at the bottom of the hill there is a low concentration of the substance if you wanted to move from a high concentration then the hill to our concentration imagine going down the hill it doesn't require energy you can just move down there however if you wanted to move from a low concentration to a high concentration then that requires energy as you would have to move up the slope so this is illustrated through this movement that we'll look at in in certain types of moving across the membrane high concentration to a low concentration does not require any energy so again imagine as ball rolling down a hill however the low concentration to the high concentration does require energy that is a active process that we'll look at in a minute so the first method of transport across the membrane that we're going to look at is diffusion the diffusion is one of the easiest to show it's the movement of molecules from an area of high concentration to an area of low concentration so as we were saying because this is going from high to low it does not require any energy it just happens you don't need to add their energy to it if you imagine something like spring and perfume in the area that you sprayed the perfume you'll smell it quite quickly people who are away from you say 10 feet away will not smell anything but as time goes on those perfume saints move through the air molecules diffuse across them and to the restroom and people can start smelling them you've no idea the energy to that you've just added the high concentration in one area of perfume and that diffuses across into areas where there's a little concentration and you start to smell it another way of showing this is if you have skittles let me look at the food coloring office kettle if you arrange some around the side of a petri dish or you can use a plate as well and fill up to about halfway up to the schedule of water what happens at the start is that the skittle has a high concentration of food coloring and the water has available concentration of food color whatever happens is diffusion takes place the food coloring moves from the high concentration of food coloring on the skittle to the low concentration and the food coloring spreads there across the water and you start seeing as nice pattern happens again you have not added any energy to this process as a passive process it just diffused across the second form of transfer across the membrane that wants to look at is almost exactly the same as diffusion however is the movement of water molecules as soon as air for mentions water molecules is osmosis so osmosis is the movement of water molecules from the area of high concentration to an area of work water concentration and it's across a selectively permeable membrane so again it's through the membrane is the movement of water molecules and to make sure you get the marks the exam make sure you're making it very clear that's high water concentration to an area of low water concentration again this is passive it's going down in the concentration gradient and it does not require any energy at all the final mode of transport that we're going to look at is the opposite of diffusion osmosis is active transport active transport is the movement of molecules or ions against the concentration gradient so what happens here is that molecules move from a low concentration of a substance to a high concentration and that will loot that before that needs to go up the concentration gradient so that requires energy this is termed an active form of transport they think of active in terms of using energy as quite a good way to remember it requires energy to go up that gradient and water also uses as the proteins found within the cell membrane is the proteins there that are responsible for moving something across or up a concentration gradient so if you just remember this diagram of what time before these large blobs of protein or what are necessary along with energy for active transport to take place in the exam there are several ways you could be asked to show your knowledge of osmosis in this section here what I've done is I've added six box beakers three of the top three down the bottom and the first three you have to look at the direction at which water will move so as Moses from a high water concentration to our water concentration so if you pause the video and for the three of the top try and identify if water would move from left to right or right to left through yours Moses okay so to go through the answer to this if we look at the first one 100% water is a higher concentration the 90% water so if you imagine these dotted lines are slightly parable membrane water moves from the left to the right it moves from high concentration to a low concentration 100 percent to 90 percent in the next one you're finally sent five percenters concentration so remove from right to left 75 to 10 and then the final one we would move from left to right 20% water as a higher water concentration than the Testament 15 percent of water submitters from left to right however down in the bottom is a bit harder because it's gave you the percentages of salt solution if we're looking at diffusion of salt molecules there should be a different situation but the question is asking you to identify the direction in which water is move so we need to change the 10% and the 5% solutions so we look at what this little percentage of water must be in the solutions so if there's 10 percent salt in the solution then there must be 90 percent water if there's 5 percent so in the solution it must be 95 percent water so what we look at here water will move from the 5 percent salt solution to the 10 percent salt solution 95 percent water to 90 percent negative 5 gram water to 90 percent water high to low in the middle one may be a same process 85 percent water or 50 percent salt to 80 percent water or 20 percent salt and finally the last one you'll find that 2.5% of salt solution has a higher water solution a higher percentage water solution than the five percent 95 percent water solution so it move from right to left always be very careful look at what the question is asking you always for osmosis or diffusion you look at high concentration to low concentration but if they give you anything other than water and say you have to identify osmosis you need to find out what the water solution is finally what we're going to look at is going back to Keira one cell biology for a brief moment you have to know you're by sight or by description what would happen to certain cells under different osmotic air conditions so if you place an animal cell into a solution with a high water concentration what would happen is water would move from the high ones water concentration outside the cell into the lower water concentration and save the cell through osmosis water it and enter the cell and the cell would swell up and it would burst eventually similarly if you put this into a low water concentration so imagine pitting an animal cell into a very high salt solution the water inside the cell would have a higher water concentration than the salty water outside so again as more thirst moves from high to low the cell would end up shrinking because the water exits the cell one thing to remember here is in the first example when the cell bursts in a high water concentration is that remember the animal cell does not have a cell wall so it has a bit less structure a bit less protection to what can happen to him that's why the cells fells up and burst the other cells you would have to look at and this would probably a bit more evident when you do the potato as Moses experiment in class if you put plant cell into high water concentration the same thing happens water moves from high water concentration outside the cell into the lower water concentration inside the cell but because the plant cell has a cell wall it doesn't burst it swells up massively the vacuole swells the cell membrane presses up against the cell wall and you can see that is physically swollen but the cell becomes something that we call target so do not see swollen you see target yes worn up but it's not bushed similarly in the low water concentration again water with exit the cell free as Moses the vacuole empties its liquid the cell membrane starts to pull away it's all very very shrunken but again we don't call it shrunken we call it plasma waste and those are two really important words to remember to get the marks if you're ever asked about osmosis in plant cells so again that is the end of kyria - here - is quite a tricky area to get your head around so again you should be using this video to be taking notes to consolidate the notes you already have from class and to be using it for a revision don't just listen to it all in one go and think you've got it go for each one pause it like answer questions try and preempt what I'm going to see I'm going to attach the quizzes and Kahoot questions for this key area you can complete in your own time on the YouTube channel but this is a list of what you need to know create the key area so as we've already looked at you need to know what the cell membrane is made up off you need to know the terms slightly parable you need to know the difference between diffusion osmosis and active transport it's important you also know the difference between what happens to animal cells and plant cells when they are exposed to high or low water concentrations thanks so much for listening I'm going to get on with the tier 3 now and upload that when we're finished